With such flow probes which can be inserted into the bore by means of, for example, an adapter provided therein, the velocity and, after suitable calibration, the volumetric flow rate of the fluid can be measured.
Unlike electromagnetic flow sensors, in which a coil assembly for producing a magnetic field passing through a measuring tube is fixed on the external surface of this measuring tube and in which at least two electrodes are provided in the wall of this tube, the electromagnetic flow probes according to the invention are inserted into a lateral bore of the measuring tube, for example, and fixed in the bore fluid-tight.
The need for the coil assembly on the external surface of the measuring tube is eliminated since the magnetic field exists only in the area of the front end of the probe, which extends into the fluid, or is produced in this area by a current flowing through the coil assembly.
U.S. Pat. No. 3,881,350 discloses an electromagnetic flow probe designed to be immersed in deep-sea water, i.e., in water under high pressures, which flows relative to the flow probe, the flow probe comprising:
a circular cylindrical housing having an outside diameter and a front end PA1 a coil assembly disposed in the housing for producing a magnetic field extending through the front plate into the fluid; PA1 a coil core disposed in the housing and made at least partially of soft magnetic material PA1 a first galvanic electrode and a second galvanic electrode disposed in the front plate on one of the diameters of the front plate and symmetrically with respect to the center of the diameter. PA1 which is designed to be immersed in a fluid flowing in a pipe, which is to be measured, the direction of immersion being virtually perpendicular to the direction of fluid flow, PA1 which is designed to be passed through a hole in a wall of the pipe fluid-tight, and PA1 which comprises: PA1 a circular cylindrical housing having a predetermined outside diameter adapted to the bore, PA1 a coil assembly disposed in the housing for establishing a magnetic field extending through the front plate into the fluid; PA1 a coil core disposed in the housing and made at least partially of soft magnetic material PA1 a first galvanic electrode and a second galvanic electrode which are disposed in the front plate on one of the meridians of the calotte and symmetrically with respect to a vertex of the meridian.
which is closed fluid-tight with a flat front plate of insulating material (this front plate referred to therein as "insulating wall"), and PA2 which is surrounded by a lenticular bead (referred to therein as "head"); PA2 which ends at or near the front plate; and PA2 the front end of the housing, which extends into the fluid, being closed fluid-tight by a front plate of insulating material in the form of a calotte, PA2 which ends at or near the front plate; and
It is obvious that because of the bead, this flow probe is not readily insertable into the bore of a pipe wall from outside fluid-tight. In the case of measuring tubes, however, but particularly in the case of installed pipes, this insertability from outside is mandatory. Thus, if the prior-art flow probe is used in a measuring tube and/or a pipe, its bead must be omitted.
Then, however, the front end of the electromagnetic flow probe terminates with the flat front plate, which must contain the electrodes. Since the fluid flows against the front end, vortices similar to those formed in vortex flow sensors are caused downstream of the front end.